CODEWITHSUNDEEP
javaswingjframe
Rubid
Rubid

Reputation: 59

Passing variables within several JFrames and classes

sorry guys, but I got confused after many hours sitting ang writting the code.

Situation:

I have two JFrames. These are different Java classes - one of them is the FirstGUI, from which we can call the other JFrame called SecondGUI. OK - that's clear. I also have one class called Processor in which i have specific methods like "connectToPort" or "disconnectFromPort".

Also, in the FirstGUI (which has the main method) I'm creating SecondGUI object (and set setVisible to false) and Processor object with FirstGUI and SecondGUI as parameters.

Problem:

From the FirstGUI in I want to call out SecondGUI (by setVisible to true) - OK, done. But what about calling out the created at the beginning Processor object from the SecondGUI JFrame? It's important to call the SAME object, because Processor methods can for example set text in the FirstGUI JFrame.JTextPane component, and add items to JComboBox of the SecondGUI.

I don't know how to solve this, I'm always getting NullPointerException.

EDIT: I want to add that I can't pass the Processor object as an argument while creating SecondGUI, because Second GUI is created earlier and it is an argument while creating Processor... That's the problem.

Upvotes: 0

Views: 887

Answers (2)

Audrius Meškauskas
Audrius Meškauskas

Reputation: 21728

When constructing the second GUI (child), the initiating class (FirstGUI) can pass self in constructor, and also retain the reference to the constructed object. Now both GUIs have the reference to each other:

class F1 extends JFrame {
   F2 child;

   void createF2() {
     child = new F2(this);
     child.setVisible(true);
   }
}

class F2 extends JFrame {
   final F1 parent;    
   F2(F1 parent) { this.parent = parent; };
}

Upvotes: 2

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285405

If you've searched out your problem or for similar problems on this site, you'll know that the most common recommendation is not to use multiple JFrames, that it is suggestive of a bad design. Better to either swap views with a CardLayout or use JDialogs of the appropriate modality.

As for your question, having one class pass information dynamically to another class, there are two main options depending on program structure.

  • If one class is in a modal JDialog, then the first class can pull information from the second modal class by calling appropriate getter methods after the second window is no longer visible.
  • If one class is displayed non-modally, then you'll want to use some type of listener such as a PropertyChangeListener to have the listening class be notified by the observed class when state changes occur.

Edit
Regarding:

From the FirstGUI in I want to call out SecondGUI (by setVisible to true) - OK, done. But what about calling out the created at the beginning Processor object from the SecondGUI JFrame? It's important to call the SAME object, because Processor methods can for example set text in the FirstGUI JFrame.JTextPane component, and add items to JComboBox of the SecondGUI.

Audrius gives you an answer for that. 1+ up-vote given to his answer.

I don't know how to solve this, I'm always getting NullPointerException.

If you get a NPE, should carefully inspect the line that throws the NPE to see which variable is null and then trace back in your code to see why. If your still stuck on a NPE and need our help, then you'll want to show pertinent code and give us more detail on the problem including noting which variable is null and why you think that it shouldn't be null.

EDIT: I want to add that I can't pass the Processor object as an argument while creating SecondGUI, because Second GUI is created earlier and it is an argument while creating Processor... That's the problem.

This is a non-issue. Since the dependent window is displayed dynamically, you can always pass a reference just prior to displaying it using a setter method.

Upvotes: 1

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